 /*******************************************************************************
  * Copyright (c) 2000, 2005 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.filebuffers;

 import java.io.IOException ;
 import java.io.InputStream ;

 import org.eclipse.jface.text.Assert;
 import org.eclipse.jface.text.BadLocationException;
 import org.eclipse.jface.text.DocumentEvent;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IDocumentListener;


 /**
  * An <code>InputStream</code> that reads from an <code>IDocument</code>.
  * The input stream ensures that its content is the same as the document
  * content when the stream was created.
  * <p>
  * Note that {@link #close()} must be called to release any acquired
  * resources.
  * </p>
  *
  * @since 3.1
  */
 class DocumentInputStream extends InputStream {

     /**
      * Document based character sequence.
      */
     private static class DocumentCharSequence implements CharSequence {

         /** Document */
         private IDocument fDocument;

         /**
          * Initialize with the sequence of characters in the given
          * document.
          *
          * @param document the document
          */
         public DocumentCharSequence(IDocument document) {
             fDocument= document;
         }

         /*
          * @see java.lang.CharSequence#length()
          */
         public int length() {
             return fDocument.getLength();
         }

         /*
          * @see java.lang.CharSequence#charAt(int)
          */
         public char charAt(int index) {
             try {
                 return fDocument.getChar(index);
             } catch (BadLocationException x) {
                 throw new IndexOutOfBoundsException (x.getLocalizedMessage());
             }
         }

         /*
          * @see java.lang.CharSequence#subSequence(int, int)
          */
         public CharSequence subSequence(int start, int end) {
             try {
                 return fDocument.get(start, end - start);
             } catch (BadLocationException x) {
                 throw new IndexOutOfBoundsException (x.getLocalizedMessage());
             }
         }
     }

     /**
      * Internal document listener.
      */
     private class InternalDocumentListener implements IDocumentListener {

         /*
          * @see org.eclipse.jface.text.IDocumentListener#documentAboutToBeChanged(org.eclipse.jface.text.DocumentEvent)
          */
         public void documentAboutToBeChanged(DocumentEvent event) {
             handleDocumentAboutToBeChanged();
         }

         /*
          * @see org.eclipse.jface.text.IDocumentListener#documentChanged(org.eclipse.jface.text.DocumentEvent)
          */
         public void documentChanged(DocumentEvent event) {
         }
     }

     /** The character sequence. */
     private volatile CharSequence fCharSequence;

     /** Document length. */
     private int fLength;

     /** The current offset. */
     private int fOffset= 0;

     /** The document. */
     private IDocument fDocument;

     /** The document listener. */
     private IDocumentListener fDocumentListener= new InternalDocumentListener();

     /**
      * Creates a new document input stream and initializes
      * the stream to read from the given document.
      *
      * @param document the document
      */
     public DocumentInputStream(IDocument document) {
         Assert.isNotNull(document);
         fDocument= document;
         fCharSequence= new DocumentCharSequence(fDocument);
         fDocument.addDocumentListener(fDocumentListener);
         fLength= fCharSequence.length();
     }

     /*
      * @see java.io.InputStream#read()
      */
     public int read() throws IOException {
         try {
             return fOffset < fLength ? fCharSequence.charAt(fOffset++) : -1;
         } catch (NullPointerException x) {
             throw new IOException (FileBuffersMessages.DocumentInputStream_error_streamClosed);
         } catch (IndexOutOfBoundsException x) {
             throw new IOException (NLSUtility.format(FileBuffersMessages.DocumentInputStream_error_read, x.getLocalizedMessage()));
         }
     }

     /*
      * @see java.io.InputStream#close()
      */
     public void close() throws IOException {
         synchronized (this) {
             fCharSequence= null;
         }
         releaseDocument();
     }

     /**
      * Copies the document prior to modification and removes the document listener.
      */
     private void handleDocumentAboutToBeChanged() {
         IDocument document= fDocument;
         if (fCharSequence == null || document == null)
             return;
         String content= document.get();
         synchronized (this) {
             if (fCharSequence == null)
                 return;
             fCharSequence= content;
         }
         releaseDocument();
     }

     /**
      * Removes the document listener.
      */
     private synchronized void releaseDocument() {
         if (fDocument != null)
             fDocument.removeDocumentListener(fDocumentListener);
         fDocument= null;
         fDocumentListener= null;
     }
 }

